Problem: Graph this system of equations and solve. $20x-8y = -40$ $-8x+8y = -8$ $1$ $2$ $3$ $4$ $5$ $6$ $7$ $8$ $9$ $10$ $\llap{-}2$ $\llap{-}3$ $\llap{-}4$ $\llap{-}5$ $\llap{-}6$ $\llap{-}7$ $\llap{-}8$ $\llap{-}9$ $\llap{-}10$ $1$ $2$ $3$ $4$ $5$ $6$ $7$ $8$ $9$ $10$ $\llap{-}2$ $\llap{-}3$ $\llap{-}4$ $\llap{-}5$ $\llap{-}6$ $\llap{-}7$ $\llap{-}8$ $\llap{-}9$ $\llap{-}10$ Click and drag the points to move the lines.
Convert the first equation, $20x-8y = -40$ , to slope-intercept form. $y = \dfrac{5}{2} x + 5$ The y-intercept for the first equation is $5$ , so the first line must pass through the point $(0, 5)$ The slope for the first equation is $\dfrac{5}{2}$ . Remember that the slope tells you rise over run. So in this case for every $5$ positions you move up You must also move $2$ positions to the right. $2$ positions to the right. $5$ positions up from $(0, 5)$ is $(2, 10)$ Graph the blue line so it passes through $(0, 5)$ and $(2, 10)$ Convert the second equation, $-8x+8y = -8$ , to slope-intercept form. $y = x - 1$ The y-intercept for the second equation is $-1$ , so the second line must pass through the point $(0, -1)$ The slope for the second equation is $1$ . Remember that the slope tells you rise over run. So in this case for every $1$ position you move up You must also move $1$ positions to the right. $1$ position to the right. $1$ position up from $(0, -1)$ is $(1, 0)$ Graph the green line so it passes through $(0, -1)$ and $(1, 0)$ The solution is the point where the two lines intersect. The lines intersect at $(-4, -5)$.